A continuously variable transmission performs power transmission by means of a V belt, for example, which is wrapped around a primary pulley into which an engine rotation is input and a secondary pulley on an output side which engages with a vehicle wheel.
In a continuously variable transmission, the step count of a step motor is controlled to realize a target speed ratio, and as a result, the pressure of the primary pulley is controlled such that a differential pressure corresponding to the target speed ratio is generated between a primary pulley pressure and a secondary pulley pressure.
In JP2004-100736A, when controlling a line pressure which serves as the source pressure of a primary pulley pressure and a secondary pulley pressure of a continuously variable transmission, a deviation in the actual step count of a step motor, occurring due to an error in the attachment of the step motor or the like, is calculated during driving as a learned value (starting learned value), and the line pressure is controlled taking the learned value into consideration, whereby an excessive or insufficient line pressure caused by an error in the attachment of the step motor or the like is corrected. Further, if a step motor control deviation, which is a deviation between the step count of the step motor corresponding to a target speed ratio and the step count of the step motor corresponding to the actual speed ratio, is large when performing steady state traveling with a set learned value, the learned value is recalculated and updated.